Process for acrylic fibers of improved properties

ABSTRACT

ACRYLIC FIBERS CONTAINING STREAKY INCLUSIONS OF 2-25% POLY(VINYL CYANOETHYL ETHER) OF DS VALUE 55-75% AND STREAKY VOIDS ARE OBTAINED BY WET-SPINNING A SOLUTION OF THE POLY(VINYL CYANOETHYL ETHER) AND THE ACRYLONITRILE IN A COMMON SOLVENT, WATER-WASHING THE WET-GEL FIBER THUS OBTAINED, STRETCHING THE WET-GEL FIBER, AND SUBSEQUENTLY DRYING THE RELAXED FIBER. THE FIBER THUS OBTAINED IS GREATLY IMPROVED IN PROPERTIES OVER COMPARABLE PRIOR ART FIBERS.

United States Patent 3,737,507 PROCESS FOR ACRYLIC FIBERS OF IMPROVED PROPERTIES Keitaro Shimoda and Isamu Obama, Okayama, Japan,

zssignors to American Cyanamid Company, Stamford,

onn. No Drawing. Filed Nov. 30, 1971, Ser. No. 203,418

Claims priority, applgcatgogl gapan, Jan. 29, 1971,

Int. Cl. D01r 7/00 U.S. Cl. 264-182 10 Claims ABSTRACT OF THE DISCLOSURE This invention relates to an improved process for obtaining an acrylic fiber containing dispersed therein as a separate but continuous phase from 2% to 25% of a poly(vinyl cyanoethyl ether), said polyether being etherified with from 55% to 75% of full theoretical etherification with acrylonitrile. More particularly, this invention relates to such process wherein prior to drying of the spun fiber but subsequent to stretching thereof, the fiber is subjected to heat-relaxation.

It is known in the prior art that improvements in acrylic fibers can be achieved by blending a poly(vinyl cyanoethyl ether) with an acrylonitrile polymer. For example, in U.S. Pat. No. 2,938,008, Hare, May 24, 1960, there is disclosed a fiber of improved properties, which fiber is based on a homogeneous blend of an acrylonitrile polymer and a poly(vinyl cyanoethyl ether). The property improvements resulting are in abrasion resistance, anti-fibrillation, and dyeability. In this reference, the polymers are not only mutually soluble in the polymer solvent but are compatible with one another in fiber form. The property improvements resulting are those associated with a homogeneous distribution of polymers throughout the fiber structure and there is no phase separation of the compatible polymers.

In our copending application Ser. No. 110,293, filed Ian. 27, 1971, now U.S. Pat. No. 3,698,994, there is disclosed an acrylic fiber comprising an acrylonitrile polymer and a poly(vinyl cyanoethyl ether), wherein the polyether is present to the extent of 2% to 25%, by weight, based on the total weight of the fiber, is etherified to the extent of 55% to 75% of full theoretical etherification with acrylonitrile, and is distributed as a separate phase within the fiber extending continuously throughout the fiber length and being detached from the acrylonitrile polymer and separated therefrom by void space. The copending application also discloses a process for preparing the fiber described, which process comprises preparing a homogeneous spinning solution in a suitable solvent of an acrylonitrile polymer and from about 2% to 25%, by weight, based on the total weight of polymer, of a poly(vinyl cyanoethyl ether) which is etherified to an extent which is from about 55% to 75 of full theoretical etherification with acrylonitrile, wet-spinning said polymer solution into a coagulant for said polymers, washing the coagulated wet-gel filaments, stretching the washed filaments and drying the stretched filaments.

Patented June 5, 1973 In accordance with the present invention, there is provided a process for producing an acrylic fiber comprising an acrylonitrile polymer and a poly(vinyl cyanoethyl ether) wherein said polyether is present to the extent of about 2% to about 25%, by weight, based on the total weight of the fiber, is etherified to the extent of about 55% to about of full theoretical etherification with acrylonitrile, and is distributed as a separate phase within the fiber extending continuously throughout the fiber length and being detached from the acrylonitrile polymer and separated therefrom by void space, which process comprises (a) preparing a homogeneous spinning solution in a suitable polymer solvent of an acrylonitrile polymer and from about 2% to about 25%, by weight, based on the total weight of polymer, of a poly(vinyl cyanoethyl ether) which is from about 55% to about 75% of full theoretical etherification with acrylonitrile, (b) wet-spinning said polymer solution into a coagulant for said polymers, (0) washing the coagulated wet-gel filaments, (d) stretching the washed filaments, (e) heatrelaxing the stretched filaments in hot water or steam, and (f) thereafter drying the heat relaxed filaments.

The process of the present invention provides fibers which are not only improved over conventional acrylic fibers in such properties as luster, hygroscopicity, and softness and have a reduced tendency to accumulate static electrical charges, but are also improved in the same properties over the fibers obtained according to the co pending application identified above. The fibers exhibit the appearance of having a streaky dispersion of the poly(vinyl cyanoethyl ether) therein, although said polyether is dispersed as a separate phase within the fiber extending continuously throughout the fiber length as a separate phase detached from the acrylonitrile polymer phase and separated therefrom by void space. The process of the present invention, by its specific application of the heat-relaxing step subsequent to stretching the wetgel filaments and prior to drying thereof, provides fibers in which the separation of the polymer phases is more pronounced and whereby greater property improvements in the fibers are achieved.

As the acrylonitrile polymer that may be employed in the present invention are included conventional fiberforming acrylonitrile polymers and more particularly those acrylonitrile polymers containing at least 70% acrylonitrile and any balance of one or more vinyl monomers copolymerizable therewith. Mixtures of such polymers may also be employed.

As the poly(vinyl cyanoethyl ethers) useful in the present invention are those having the formula Lu J.

wherein m+n represents the total content of the polymer and m represents from about 55% to about 75 of the total content and R represents hydrogen or an acetyl group. The molecular weight of the polymer may vary widely and is not critical. Typically, polymers corresponding to those wherein the unsubstituted polyvinyl alcohol has a molecular weight in the range of about 10,000 to about 100,000 are employed.

A customary procedure for obtaining a poly(vinyl alcohol) is by polymerizing vinyl acetate and subsequently saponifying the resulting polymer. The percentage of by droxyl groups produced will depend upon the degree to which saponification is efiected. To obtain the cyanoethyl ether, the saponified poly(vinyl acetate) is reacted with acrylonitrile under alkaline conditions and, since such conditions also effect saponification, it is possible to efiect saponification and etherification concurrently. Thus, the useful poly(vinyl cyanoethyl ethers) are readily obtained by controlled saponification and etherification of poly- (vinyl acetate). As stated above, the usage of poly(vinyl cyanoethyl ether) must be between about 2% and 25%, by weight, based on the total polymer weight.

If the value of m in the formula given above is less than about 55%, the poly(vinyl cyanoethyl ether) is dissolved out of the extruded filament in the coagulating bath, in the washing step immediately following, or both and will not be present in the final fiber. On the other hand, if the value of m is greater than about 75%, the poly(vinyl cyanoethyl ether) will become compatible with the acrylonitrile and the desired separate and detached phase will not be obtained. If the content of poly(vinyl cyanoethyl ether) is less than about 2%, by weight, based on the total weight of polymer, such content does not effect any significant improvements in the resulting fiber properties. On the other hand, if the content of poly (vinyl cyanoethyl ether) is above about 25 by weight, based on the total weight of polymer, the swollen gel fibers upon drying, regardless of drying temperature, tend to stick together, apparently due to inability to confine the poly (vinyl cyanoethyl ether) as a separate phase within the fiber.

As the solvent for preparing the spinning solution of the polymers, one may use organic solvents or inorganic salt and inorganic acid solvents. As organic solvents, for example, one may use dimethyl formamide, dimethyl acetamide, and dimethyl sulfoxide. As inorganic salt solvents, for example, one may use concentrated aqueous solutions of thiocyanates, such as sodium, potassium, ammonium and calcium thiocyanates and mixtures thereof, concentrated aqueous solutions of Zinc chloride, and concentrated aqueous solutions of lithium chloride. As inorganic acid solutions, for example, one may use concentrated aqueous nitric and sulfuric acids.

As the coagulant for the spun polymer solution, typically one uses those liquid coagulants normally employed in wet-spinning, taking into account those subtle relationships between polymer solvent and coagulant as are well known in the art. Among the suitable coagulants, for example, are water, aqueous solutions of the above mentioned inorganic salts or acids in which the concentration of salt or acid does not exceed 20% by weight thereof, aqueous solutions of the above-mentioned organic solvents in which the concentration of organic solvent is in the range of 20% to 70% by weight thereof, or polyethylene glycol.

In carrying out the process of the present invention, a spinning solution is prepared by dissolving the acrylonitrile polymer and poly(vinyl cyanoethyl ether) in the selected polymer solvent. Preferably, this solution is prepared by first dissolving the poly(vinyl cyanoethyl ether) in at least a portion of the selected solvent and then adding the acrylonitrile polymer, while making any necessary adjustment as to solvent content. It is generally preferable to adjust the polymer content of the spinning solution to between about 10% and 30%, by weight, based on the total weight of the spinning solution. However, it is not necessary to restrict the polymer content of the spinning solution to this specific range since such factors as solution viscosity, temperature of the spinning solution, and

solvent nature influence the useful polymer concentrations in specific instances.

The polymer solution is wet-spun into an appropriate coagulant according to conventional procedures. Following coagulation, the filaments are washed and stretched in accordance with conventional procedures. The stretched filaments, in accordance with the present invention, are then subjected to heat relaxation in hot water or steam. When the relaxed filaments are then subsequently dried, they are rapidly dehydrated to yield highly desirable fibers. The amount of water in the swollen gel fiber subjected to twat el ati n sh u t be g ater ha 2 p ferabl 50%, by weight, based on the total weight of the gel fiber.

In the event the amount of water contained in the gel fiber is less than 25 the operation and effect peculiar to the present invention and caused by heat-relaxing the wet-spun fiber filament substantially in a swollen state with hot water or steam, that is, the dispersion of the poly (vinyl cyanoethyl ether) in the form of streaks and the formation of voids in the fiber structure by quick dehydration will become exceedingly difficult to achieve and such physical properties of the fiber as luster and hygroscopicity will be reduced.

The conditions under which heat relaxation of the stretched wet-gel fibers is carried out generally involve temperatures in the range of -150 C. for from 5-30 minutes, or preferably in steam at -120 C. for 520 minutes. In the event the temperature is below about 80 C., it will be difiicult to eflect substantial relaxation of the filaments quickly and the separation of polymer phases and the generation of spot-like voids in the fiber will be obstructed and the effectiveness of the present invention will be reduced. In the event the treating temperature is above about 150 C., discoloration of the fiber will tend to occur and such is not desirable.

The fiber that has been thus heat-relaxed is then dried at a temperature ranging from room temperature (i.e. 20-25 C.) to about 130 C., preferably 90 to C. to obtain the final fiber. In the event the temperature exceeds about C., the voids formed in the fiber structure during the heat-relaxing step will collapse and a reduction of final fiber luster will ensue.

Although it is not known for certain what mechanism is responsible for the fibers of the present invention and the inventors do not wish to be bound by any particular theory, the following theory is suggested. Both polymers are coagulated by the coagulating bath as it penetrates into the extruded polymer solution but the rate of coagulation differs among the two polymers. The acrylonitrile polymer coagulates first upon contact with the coagulant and forms the outer periphery of the wet-gel filament. Since the poly(vinyl cyanoethyl ether) is incompatible with the coagulated acrylonitrile polymer and is not immediately precipitated by the coagulant, the poly(vinyl cyanoethyl ether) in solution form is displaced toward the center of the filament by the penetrating coagulant and the increasing content of coagulated polyacrylonitrile building up within the peripheral wall of the gel filament. Although the coagulant can penetrate the porous nature of the gel filament, the poly(vinyl cyanoethyl ether) is incapable of such penetration and remains within the gel structure. Eventually, as coagulation. continues, the poly (vinyl cyanoethyl ether) is coagulated within the fiber as a separate phase from the acrylonitrile polymer but, because the poly(vinyl cyanoethyl ether) remained as an interconnected solution within the gel filament, the poly (vinyl cyanoethyl ether) phase remains connected along the length of the formed filament. As first formed, the separate poly(vinyl cyanoethyl ether) phase is joined to the inner portion of the acrylonitrile phase. Subsequently after washing, stretching, heat relaxation in particular, and drying, due to differences in the swollen states of the polymers and differential shrinkages thereof, the poly- (vinyl cyanoethyl ether) becomes detached from the acrylonitrile polymer and void space forms between the polymer structures. This ultimate structure is felt to give rise to the streaky dispersion effect noted. It is also felt that the unique structure of the fiber gives rise to the improved properties noted.

In accordance with the process of the present invention wherein the provision is made for heat relaxation of the stretched wet-gel filament prior to drying, the rapid dehydration achieved results in a more pronounced polymer layer separation than in the process of the copending application identified above and streaky voids are more copiously generated along the layer of pol y(vinyl cyanq.

ethyl ether) and even in the acrylonitrile polymer layer, which is the main fiber-forming component, many spotlike voids will be generated.

Due to streaky inclusion of poly(vinyl cyanoethyl ether) within the acrylic polymer structure and the high level of voids generated by the heat-treating step, the resulting acrylic fiber is remarkably improved in such fiber properties as luster, hygroscopicity, softness and resistance to static electrical build-ups.

The invention is more fully illustrated by the examples which follow in which all parts and percentages are by weight unless otherwise stated.

The various tests by which the data recorded in the following examples are obtained are conducted as follows.

(1) K/S value 1.5 grams of the fiber to be measured are immersed in a solution at 70 C. of the following:

0.5% of 0.1. Basic Blue 22 1.0% of acetic acid 10.0% of sodium sulfate wherein the percentages are based on the weight of fibers. The volume of solution is 50 times the weight of fibers. Upon immersion of the fibers, the bath is heated to 100 C. at the rate of 1 C. per minute and the bath is then maintained at 100 C. for 30 minutes. The fibers are then gradually cooled in the bath, removed, and dried. One gram of the dyed fibers are then taken and the reflectance determined using a source of monochromatic light. The K/S value is determined from the Kubelka-Munk equation:

K/S=(1R) /2R wherein R is the reflectance measured, K is the absorption coefficient of the fibers and S is the scattering coefficient of the fibers.

The K/S value quantitatively represents the magnitude of the internal reflecting surface area and smaller K/S values indicate larger internal reflecting surface areas. Thus, the K/S value indicates the degree of streaky dispersion formed within the fibers by the poly(vinyl cyanoethyl ether).

(2) 60-degree Mirror Surface Luster Samples of fiber from which any crimp has been removed are arranged in parallel and laid flat on a cardboard to present a rectangular fiber surface of size 6 centimeters by 4.5 centimeters. The 60-degree Mirror Surface Luster is then determined according to the method described in HS 2-8741 using a GM-S luster meter (manufactured by Murakami Color Technical Laboratory). Measurements of luster were obtained with the angle of incidence parallel to the axial direction of the fiber.

(3) Hygroscopicity About 2 grams of fibers to be measured are predried for one hour at 80 C. and then conditioned at 20 C. and 65% relative humidity for 24 hours. The condition fibers are weighed and the weight designated as A. The fibers are then dried for 20 hours at 60 C. at a. pressure equivalent to 50 millimeters of mercury employing a vacuum dryer containing phosphorus pentoxide. The fibers thus dried are weighed and the weight designated B. The hygroscopicity is calculated from the following formula employing the weights designated above:

Hygroscopicity (percent) X 100 (4) Antistatic activity The fibers are conditioned for 16 hours at 20 C. and 65% relative humidity. The electrical resistivity of the fiber surface is then measured using an appropriate meter (Textrome Model GR-54, manufactured by Chuo Electronic Industrial Company, Ltd.).

(5 Softness The fiber was evaluated by a panel of 10 judges skilled in the art of evaluating softness and the results given are based on these evaluations.

EXAMPLE 1 A poly(vinyl acetate) which had been saponified to an extent which exceeds was employed in preparing a poly(vinyl cyanoethyl ether). The polymer had a degree of polymerization of 1700, i.e. a molecular weight of about 75,000. One part of the polymer was dissolved in 10 parts of 1% aqueous sodium hydroxide solution. To this solution were added 2.5 parts of acrylonitrile and reaction eflfected at 50 C. for 150 minutes. The resulting polymer was filtered and water-washed to prepare a poly (vinyl cyanoethyl ether) which contained 71.2% of full theoretical content of cyanoethyl groups and 45% water.

One part of the obtained poly(vinyl cyanoethyl ether) was dissolved in 7.2 parts of 60% aqueous sodium thiocyanate solution. As the acrylonitrile polymer there was employed a copolymer of the following monomer composition:

91 acrylonitrile 8.73% methyl acrylate 0.27% sodium methyllylsulfonate Nine parts of this polymer and 6.9 parts of water were added to the solution of polyether and stirred to obtain a uniform slurry. To the slurry was then added 24.1 parts of 60% aqueous sodium thiocyanate solution and the mixture was stirred at 60 C. for 75 minutes to obtain a clear solution. The solution obtained, which had a ratio of acrylonitrile polymer to poly(vinyl cyanoethyl ether) of 90: 10, respectively, was heated to 75 C., spun through a spinnerette into an aqueous coagulation bath which consisted of a 12% aqueous solution of sodium thiocyanate maintained at a temperature of 3 C. The filaments thus formed were water-washed while being stretched at a stretch ratio of 2:1 and then further stretched in boiling water at a stretch ratio of 5:1. The stretched fibers were then passed through squeeze rolls to adjust the water content of the filaments to 150%. The gel fiber filament was heat-relaxed with steam at C. for 15 minutes and then dried at 90 C. Fiber properties are given in Table I.

EXAMPLE 2 The procedure of Example 1 was followed in every material detail except that the stretched gel fiber filament was heat-relaxed in boiling water for 15 minutes prior to drying at 90 C. Fiber properties are also given in Table I.

Comparative Example A The procedure of Example 1 was followed in every material detail except that the fiber immediately after stretching in boiling water was dried at 90 C. to a water content of 6% and was then heat-relaxed in steam at 110 C. for 15 minutes. Fiber properties are also given in Table I.

Comparative Example B A spinning solution was prepared by dissolving 10 parts of the acrylonitrile polymer of Example 1 in 90 parts of an aqueous solution of 48% sodium thiocyanate. The fiber was processed as in Example 1 up to and including stretching in boiling water. At this point the fiber was next dried at a dry bulb temperature of C. and a relative humidity of 20%. The fiber was then heat-relaxed in saturated steam at 120 C. for 10 minutes. Fiber properties are also given in Table I.

TABLE I Fiber from Example- Flber property 1 2 Comp. A Comp. B

K/S value 0. 48 0. 458 1. 003 1. 600 Hygroscopicity 3. 6 3. 3 3. 3 1.2 60 degree mirror surface luster 54 56 45 33 Surface resistivity (ohms)-.- 10 10 10 10 Softness ratings of fibers from Examples 1, 2 and Comparative Example A were considerably better than that of fiber from Comparative Example B.

The results given in Table I indicate that fibers obtained by the process of the present invention have vastly improved properties over comparable prior art fibers containing no poly(vinyl cyanoethyl ether) therein and also have improved properties over the fibers obtained according to the prior process wherein the fibers are dried prior to heat relaxation.

EXAMPLE 3 One part of a poly(vinyl cyanoethyl ether) prepared as in Example 1 was dissolved in 5.15 parts of a 60% aqueous solution of sodium thiocyanate. 3.9 parts of a homopolymer of acrylonitrile containing 20% Water was added to the solution along with 5.77 parts of water to form a slurry. To the slurry was added 15.82 parts of a 60% aqueous sodium thiocyanate solution. The mixture thus obtained was agitated at 60 C. for 75 minutes to form a clear spinning solution wherein the acrylonitrile polymer and poly(vinyl cyanoethyl ether) were present in 85:15 ratio, respectively.

The spinning solution was heated to 70 C. and spun through a spinnerette into a coagulant consisting of a 12% aqueous solution of sodium thiocyanate at -3 C. The spun filament was water-Washed while being stretched at a stretch ratio of 2:1. The filaments were then stretched in boiling water at a stretch ratio of 5:1 and then heatrelaxed for 15 minutes in steam at 115 C. The steamed fiber was then dried at 90 C. Fiber properties are given in Table II.

Comparative Example C TABLE 11 Fiber from Example- Fiber properties 3 Comp.

K /S value 0. 620 1. 335 60 degree mirror surface luster 56 16 The results given in Table -II show that without the presence of the streaky dispersion of poly(vinyl cyanoethyl ether) in the fiber, the improved fiber properties are not obtained.

EXAMPLE 4 The procedure of Example 1 was followed in every material detail except that the ratio of acrylonitrile polymer to poly(vinyl cyanoethyl ether) was 98:2 respectively. This ratio was obtained by dissolving 1 part of the polyether prepared in Example 1 and 361 parts of a 60% aqueous solution of sodium thiocyanate and adding 49 parts of the acrylonitrile polymer of Example 1 thereto. The resulting mixture was agitated at 60 C. for 75 minutes to obtain a clear spinning solution.

The fiber spun and processed following the procedure of Example 1 exhibited a K/S value of 0.74.

EXAMPLES AND 6 The procedure of Example 1 was followed in every materia de ai ex pt tha p or o heat-relaxing the fiber of Example 5 was squeezed to a water content of 25% and that of Example 6 was squeezed to a water content of 200%. Fiber properties are given in Table III.

1. A process for producing an acrylic fiber comprising an acrylonitrile polymer and a poly(vinyl cyanoethyl ether), wherein said polyether is present to the extent of about 2% to about 25%, by weight, based on the total weight of the fiber, is etherified to the extent of about 55% to about 75% of full theoretical etherification with acrylonitrile, and is distributed as a separate phase within the fiber extending continuously throughout the fiber length and being detached from the acrylonitrile polymer and separated therefrom by void space, which process comprises: (a) preparing a homogeneous spinning solution in a suitable polymer solvent of an acrylonitrile polymer containing at least 70% acrylonitrile and any balance of one or more vinyl monomers copolymerizable therewith and from about 2% to 25%, by weight, based on the total weight of polymers, of a poly(vinyl cyanoethyl ether) which is from about 55% to about 75% of full theoretical etherification with acrylonitrile and the balance is in the form of the alcohol or the acetate ester thereof, said polyether having a molecular Weight in the range of about 10,000 to about 100,000; (b) wet-spinning said polymer solution into a coagulant for said polymers; (c) washing the coagulated wet-gel filaments; (d) stretching the washed filaments; (e) heat-relaxing the stretched filaments in hot water or steam; and thereafter drying the heat-relaxed filaments.

2. The process of claim 1 wherein the water content of the wet-gel filament subjected to heat relaxation is at least 50%, by weight, based on the total weight of said wet-gel filament.

3. The process of claim 1 wherein the temperature of heat relaxation is in the range of C. to 150 C.

4. The process of claim 1 wherein the heat relaxation is accomplished with steam at a temperature of C.

5. The process of claim 1 wherein said drying is accomplished at a temperature in the range of 90120 C.

6. The process of claim 1 wherein partial stretching of the wet-gel filament is accomplished during the washing step.

7. The process of claim 1 wherein the acrylonitrile polymer contains at least 70% of acrylonitrile and any balance of one or more vinyl monomers copolymerizable therewith.

8. The process of claim 1 wherein the acrylonitrile polymer is a homopolymer.

9. The process of claim 1 wherein the polymer solvent is a concentrated aqueous thiocyanate salt solution.

10. The process of claim 9 wherein the polymer coagulant is an aqueous thiocyanate salt solution.

References Cited UNITED STATES PATENTS 2,341,553 1943 =Houtz 264-182 2,938,008 5/ 1960 Hare 260-326 3,384,694 5/1968 Nakayama et al. 264-290 3,426,117 2/1969 Shimoda et al. 264-210F 3,451,140 6/1969 Nakayama et al. 264-182 3,514,512 5/1970 Kikuchi et al. 264-182 JAY H. WOO, Primary Examiner U- CL X-R. 264-2l0F 

